Electrophotographic organic photoconductors



- characteristics. ous polymeric substance are dissolved together in such United States Patent 3,290,147 ELECTROPHOTOGRAPHIC ORGANIC PHOTOCONDUCTORS John Alan Mattor, Gorham, Dumont Biglar Henderson, Portland, and Ben Millard, Windham, Maine, assignors to S. D. Warren Company, Boston, Mass, a corporation of Massachusetts No Drawing. Filed Aug. 7, 1963, Ser. No. 300,617 5 Claims. (Cl. 96-1) The present invention relates to photographic reproduction, and more especially to an electrophotographic process utilizing the photoconductive characteristics of a certain class of organic compounds, the N-disubstituted benzylideneazines, to produce the electrostatic latent image.

In an electrophotographic process, a non-visible charge pattern is developed on the electrophotographic plate. The plate consists of a coating of photoconductive insulating layer on a carrier such as paper, aluminum plate, or plastic. The photoconductive insulating layer is electrically charged as with a corona discharge so that the coating has a uniform positive or negative charge on its surface. The plate is than exposed to a light image. The charge density obtained at any point on the photoconductive insulating layer is related to the intensity of illumination obtained at that point during the exposure. The image is then developed with an electrostatically attractable toner in a known manner. The developed image, composed of colored pigment, together with a thermoplastic resin, is subsequently fixed by heating, or in the-case of liquid toners by the air oxidation of the drying oils. 1

In recent years, many investigations have been made with respect to the nature of suitable carriers and of photoconductive materials to be coated thereon. Most notable among photoconductive substances hitherto applied to the electrophotographic process have been inorganic materials such as zinc oxide and selenium.

The present invention is based on the finding that a class of organic compounds, the N-disubstituted benzylideneazines, are excellent photoconductive materials for use in the preparation of electrophotographic plates. These compounds have good photoconductivity and are particularly suitable for the preparation of lithographic plates as well as for use in desk type ofiice copying devices, or electrophotographic printing. The compounds of this class are, in general, stable compounds with a long shelf life and are soluble in most common resin binder-solvent systems so that they can be readily applied to the supporting substrate.

The photoconductive substances which are used according to this invention for the preparation of electrophotographic copy are preferably used in association with clear resinous polymeric binders having high dielectric characteristics such as polystyrene, polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, polyvinyl acetals, polyvinyl ethers, polyacrylic esters, or any other natural or synthetic polymeric substance having the proper electrical The organic photoconductor and resinorganic solvents as benzene, toluene, methyl ethyl ketone, methyl isobutyl ketone, chloroform or methylene chloride. Mixtures of two or more photoconductive substances may be used, as well as mixtures of two or more mutually miscible solvents which will utilize with the greatest efiiciency the solubilities of both the photoconductor and the resinous binder. are coated on a suitable carrier and, when dried, form a solid solution which is transparent.

The solvent solutions The electrophotographic plate of this invention com- 3,290,147 Patented Dec. 6, 1966 (1) CaHs H H C2115 02 i; oz s MLP, 1S8.5-1S9.0 C.

( CH3 H H CH;

on, on,

M.P. 250-253 C. (Bell. 14:, 36) (3) CzHs caHs M.P. 207209 C.

-CH1 H H CH7 I l N C=NN=C N -CH2 CHz M.P. 182.6183 C.

ning, 1 1 1 1 7 ac CHQOHZ CHzCHz M.P. greater than 245 C.

Queen-cg n 1? on.=cn=on.

. CH3 CH5 M.P. 145.0146.5 C. (8)

C2115 2 Calls M.P. 197.5 to 198.5 C.

() CgHs Of the above 17 examples, compounds 5, 8, 12, 13 and 17 are preferred examples from the standpoints of solubility and sensitivity. It will 'be noted that in all cases the compound is symmetrical and the aryl radical is either phenyl or naphthyl with the N-substituted amine being in the para position in the case of the phenyl radical and in the 6 position in the case of the naphthyl radical. Also, the nitrogen group is a tertiary amine with the two terminal substituents thereon being straight chain alkyl or alkylene radical of 1 to 3 carbon atoms each or alkyl radicals of 1 to 2 carbon atoms each terminally substituted with halogen or phenyl group.

The preferred photoconductive compounds of the invention have the formula:

where A is a phenyl radical substituted in the para position with the nitrogen or naphthyl group substituted in the 4, 5, 6 or 7 position with the nitrogen. The phenyl group can be additionally substituted in the ortho, but not meta position with such groups as alkyls of 1 to 3 carbon atoms, nitroso, acyl and halogen, and the naphthyl radical can likewise be substituted in the 4, 5, 6 or 7 position. R in the formula is an alkyl or alkylene radical of 1 to 3 carbon atoms which can contain a terminally attached phenyl, halogen or hydroxyl group or can be part of a ring system. The melting points of the preferred compounds is in the range of 99 to 250 C. and their molecular weight is in the range of 294 to 578.

The compounds of this invention are prepared by the condensation of the corresponding N-disubstituted aryl aldehydes with hydrazine. An example of this type of reaction is the preparation of bis-4, 4'-dimethylamino benzylideneazine as found in Beilstein 14, 36.

The aforementioned compounds dissolved in a layer of insulating resin charged and exposed with light in the Wave-length range from 3500 to 4200 Angstroms will produce electrostatic latent images as previously described. Excellent images may be obtained by a short exposure under a photographic transparency using a carbon arch or mercury-vapor lamp. The surface will hold a charge of 100 to 400 volts.

It has been discovered, however, the spectral sensitivity may be shifted into the visible region and'the sensitivity increased to the extent that images may be formed by using a low wattage tungsten lamp. Further, the sensitivity is such that images may be formed in reasonable exposure times using projection techniques. This spectral sensitivity is obtained by adding to the photoconductor-resin mixture a small amount of dyestuff such as Crystal Violet, Cryptocyanine, Pinacyanole, Orthochrome T, Rhodamine B, or Sulforhodamine. See also page 8 of British Patent No.'. 895,001 (1962). Water soluble quaternary ammonium and oxonium dyes are preferred.

The invention is further illustrated in the following specific examples, without being limited thereto:

Example I A solution containing 1 g. of bis-4,4'-diallylamino ben- Zylideneazine (Formula 12 above), 2.5 g. of B-76 (a polyvinyl butyral polymer made by Shawinigan Chemicals Corporation of Springfield, Massachusetts), 50 mg. of Crystal Violet, and 50 ml. of methyl ethyl ketone is applied with a Meyer bar or other suitable means to a piece of paper, applying a coating weight of 1 to 3 pounds (dry solids) per ream (500 sheets, 25 by 38 inches) of paper. For best results, the paper used should be pretreated with a mineral pigment coating, bound with a hydrophilic adhesive, to insure minimum penetration of the organic solvent into the sheet. The pretreated paper, thus coated, is allowed to air dry or is dried for several minutes in an oven at 60 to 100 C. Direct images are produced on the sheet of paper by the electrophotographic process in the following manner: the coated paper is either positively or negatively charged under a corona discharge and then exposed under a positive or negative transparency with a light source such as a. 60-watt tungsten lamp. Immediately after exposure, a dry electrostatically attractable resinous toner, colored with a pigment, is applied to the sheet. For best results, this is done in a reduced light area, preferably under a red light. The toner thus applied adheres to the parts of the coating which have not been exposed to the light and a positive image appears. The image sheet is then heated for a short period at 100-130 C. to fuse the resin and fix the image.

If aluminum, plastic foil, or a suitable grade of paper is used as a carrier for the coating, the images may be used as master copies for any sort of lithographic duplicating process, provided the non-image areas are treated to make them ink repellent and water receptive. In this process, for example, a sheet of paper which has been pretreated to give a hydrophilic surface, e.g. a surface coating composed of titanium dioxide, carboxymethylhydroxyethyl cellulose or similar water soluble cellulose derivative, and melamine formaldehyde resin (see U.S. Patents, 2,778,735 and 2,778,301) is coated with a solution consisting of 1.0 g. of bis-4,4'-diethylamino benzylideneazine (Formula 1), 2.5 g. of B76 resin, 50 mg. of Rhodamine B, and 50 ml. of chloroform. The sheet is dried, then charged and imaged in the above manner and fused at 140l60 C. The surface of the sheet is then washed with methanol, ethanol, iso-propanol, or mixtures of same, thereby exposing again the hydrophilic surface in all areas but the hydrophobic image areas. The sheet thus formed may .be used in any type of hydrophilic-hydrophobic lithographic duplicating process.

In addition to the above solvents, mixtures of syrupy phosphoric acid with alcohols, with or without small amounts of stronger mineral acids such as hydrochloric or sulfuric have proved to be excellent wash solutions. The photoconductive compounds of this invention are acid soluble and the acid-alcohol mixture dissolves them in the non-image area Where they are not protected by the resinous toner. This opens up the resin binder to attack and removal by the solvent. The acid also renders the thus exposed non-image areas hydrophilic.

Example II A solution consisting of 1.0 g. of bis-4,4-diethylamino- 2,2'-dirnethyl benzylideneazine (Formula 3), 2.5 g. of B76 resin, 50 mg, of Cryptocyanine, and 50 ml. of chloroform is coated in the above manner on a pretreated sheet of paper. The electrophotographic process for imaging the sheet and results are the same as described in Example I.

Example III A solution consisting of 1.0 g. of bis-4,4-dibenzylamino benzylideneazine (Formula 5), 2.5 g. of VYLF resin (a copolymer consisting of 87% vinyl chloride and 13% vinyl acetate made by Union Carbide and Carbon Chemical Corp.) and 50 mg. of Rhodamine B is dissolved in a mixture of 25 ml. of chloroform and 25 ml. of methyl ethyl ketone, and is coated in the previously described manner on a pretreated sheet of paper (2 coats) and on aluminum foil (1 coat). The electrophotographic process fifl imaging the sheet is the same as described in Examp e I.

Example IV A solution consisting of 1.0 g. of bis-4,4'-ally1methy1- amino benzylideneazine (Formula 7), 2.5 g. of VMCH resin (a copolymer consisting of 86% vinyl chloride and 13% vinyl acetate made by Union Carbide), 50 mg. of Orthochrome T and 50 ml. of methyl isobutyl ketone is coated on pretreated paper, plastic or metal foil as previously described. The direct image is formed as described in Example I.

Example V A solution consisting of 0.5 g. of bis-4,4-diethylamino- 2,2',6,6-tetrachloro benzylideneazine (Formula 9), 0.5 g. of bis-4,4'-morpholynyl benzylideneazine (Formula 6), 2.5 g. B-76 resin, 50 mg. of Rhodamine B, and 50 ml. of chloroform is coated on pretreated paper, plastic or metal foil as previously described. The direct image is formed as in Example I.

Example VI A solution consisting of 1.0 g. bis-4,4'-diallylamino benzylideneazine (Formula 12), 2.0 g. of polyvinylidene chloride and 25 mgs. of Pinacyanole is dissolved in 50 ml. of methyl ethyl ketone, and coated on pretreated paper, plastic or metal foil as previously described. The electrophotographic process for imaging the sheet is the same as described in Example I.

Having described this invention, what is sought to be protected by Letters Patent is succinctly set out in the following claims:

1. An electrophotogr-aphic copy sheet comprising a photoconductive insulating layer on a conductive support, the photoconductive layer containing a photoconductive compound selected irom the class of compounds known as arylideneazines and having the general formula:

H R1(IJ=N--N=(IJR1 wherein R and R are N-disubstituted aryl radicals.

2. An electrophotographic copy sheet according to claim 1 in which the photoconductive layer also contains a dye sensitizer.

3'. An electrophotographic material according to claim 1 in which the photoconductive layer essentially consists of a clear resinous binder and said photoconductive compound.

4. An electrophotographic copy sheet comprising a photoconductive insulating layer on a conductive support, the photo-conductive layer containing a compound selected from the class of compounds known as arylideneazines and having the general formula:

wherein Ar is selected from the group consisting of phenyl radicals substituted in the para position with the nitrogen and nap'htlhyl nadicals substituted in the 4, 5, 6 or 7 position with the nitrogen, and R is selected from the group consisting of alkyl and al kylene radicals, said compounds having a melting point in the range of 99 to 25-0 C. and a molecular weight in the range of 294 to 578.

5. An electrophotograp hic copy sheet comprising a photoconductive insulating layer on a conductive support, the photoconductive layer containing a compound selected from the class of compounds known as arylideneazines and having the general formula:

R1C=NN=CR1 wherein R is a phenyl radical substituted in the para position with N (R and in the ortho position with a radical selected from the group consisting of methyl and ohloro radicals, and where R is a hydrocarbon group.

References Cited by the Examiner UNITED STATES PATENTS 3,041,165 6/1962 Sus et al. 96-1 3,066,023 11/ 1962 Schlesinger 96-1 NORMAN G. TORCHIN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 290, 147 December 6, 1966 John Alan Mattor et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, formula "(7)" should appear as shown below instead of as in the patent:

CH2=CH-CH2\ CHZ=CH=CH2 M.P. 145 0-146. 5 C.

column 3, formula "(11) should appear as shown below instead of as in the patent:

M.P. greater than 25 C. (darkens) Signed and sealed this 21st day of November 1967 (SEAL) Attest:

EDWARD M. FLETCHER,JR. Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

1. AN ELECTROPHOTOGRAPHIC COPY SHEET COMPRISING A PHOTOCONDUCTIVE INSULATING LAYER ON A CONDUCTIVE SUPPORT, THE PHOTOCONDUCTIVE LAYER CONTAINING A PHOTOCONDUCTIVE COMPOUND SELECTED FROM THE CLASS OF COMPOUNDS KNOWN AS ARYLIDENEAZINES AND HAVING THE GENERAL FORMULA: 